Locomotor - bone and the skeleton

Question 1

What is bone?

Answer 1

Osseous living tissue containing specialised cells and a matrix of:
- 60% mineral salts (hydroxyapetite)
-35% collagen (type I)
- 4% water
-1% proteoglycan

Question 2

What are the functions of bone?

Answer 2

Housing stem cells (bone marrow)
Provide structural support and locomotion
Acting as a reservoir of minerals
Providing protection of underlying structures
Bufferin excessive pH changes in the blood
Production of blood cells
Regulating electrolyte body balance (Ca and P ions)

Question 3

What classifies a long bone?

Answer 3

Classified as longer than it is wide, adapted to work as a lever.

Question 4

What is the end of the long bone?

Answer 4

Called an epiphysis.

Rounded and covered with articular cartilage, which sits on top of subcondral bone and below a layer of cortical bone.

This is supplied by red bone marrow.

Question 5

What is the middle of the long bone?

Answer 5

Called the diaphysis.

Formed of cortical bone surrounding a medullary cavity. It is filled with yellow bone marrow and has own blood supply via vessels through the nutrient foramen.

Question 6

What is the metaphysis?

Answer 6

Between the diaphysis and epiphysis. Where the epiphyseal plate sits.

Question 7

What makes up the medullary cavity?

Answer 7

Lined by the endosteum - single layer of cells

Is osteogenic and osteolytic.

Question 8

What covers the outside of the bone?

Answer 8

Periosteum covers it. 2-layers for protection and site of sensory nerves, blood and lymphatic vessels.

Question 9

What are short/irregular bones?

Answer 9

Short - same width and length
Irregular - complex shapes

No medullary cavity
Develop from single site of ossification

Question 10

What are flat bones?

Answer 10

Thin and broad bones found where extensive organ protection is required or broad surface for muscle attachment.

No medullary cavity
2 layers of bone surrounding air or trabecular

Question 11

Whats an example of long bones?

Answer 11

Arm bones
-humerus, ulna, radius, metacarpals and phalanges
Leg bones
-femur, tibia, fibia, metatarsals and phalanges

Question 12

What are examples of short bones?

Answer 12

Tarsals, carpals and patella

Question 13

What are examples of irregular bones?

Answer 13

Vertebrae, sacrum (middle of the pelvis where joins vertebrae), coccyx and some bones of the skull

Question 14

What are examples of flat bones?

Answer 14

Thoracic cage
Pectoral girdle (scapular, collar bones and ribs)
Pelvis (ilium, iscium and pubis)
Some skull bones

Question 15

What are examples of sesamoid bone?

Answer 15

Patella bone
Bones near joins in knees, hands and feet

Question 16

What is the blood supply of bones?

Answer 16

Cortical - well vascularised via arteries that enter the bone via nutrient foramen in the diaphysis. Supply the calcified cartilage.

Travels horizontally via Volksmann canals and vertically via Haversian canals.

Question 17

What are osteons?

Answer 17

Layers of lamella bone and osteocytes around the blood vessels.

Question 18

What is lamella formed of?

Answer 18

Cortical bone (type I collagen), twists in opposite directions,

Question 19

What gives lamella its strength?

Answer 19

Collagen orientation
-Transverse: compression
-Longitudinal: tension

Structural integrity gives some reisitance to twisting

Question 20

What are the two types of bones formed?

Answer 20

Lamella - regular, strong bone slowly produced during growth/remodelling

Woven bone - weak, irregular bone, produced rapidly in early life/healing. It’s gradually replaced by lamella bone.

Question 21

What are osteoblasts?

Answer 21

They form bone matrix (osteogenic activity).

Cuboidal cells found in periosteum secrete osteoid which becomes bone matrix/osteocytes when trapped

Question 22

What are osteocytes?

Answer 22

Formed bone matrix, maintain bone structure and influenced by environment. Important with:
-Maintenance of local matrix and acts as mechanoreceptors

-Resorb material during passive bone resorption and Ca/O homeostasis

-Communicate between osteocytes and osteoblasts

Question 23

What are osteoclasts?

Answer 23

Absorb bone matrix via enzymes and hydrogen ions. Look like large multinucleated cells. Originate from haematopoietic tissue.

Question 24

What is endochrondrial ossification?

Answer 24

1. Bone is formed onto a temporary cartilage model
2. The model grows (zones of proliferation), then chondrocytes mature and hypertrophy, and growing cartilage model calcifies
3. As this happens chrondrocytes start to die. Fragmented calcified matrix left behind acts as structural framework
4. Blood vessels and chrondrocytes invade and osteoblasts lay down bone matrix

In foetus the primary ossification centre forms in diaphysis and a secondary in epiphysis. All replaced by cartilage, except epiphyseal plate which stays open till maturity.

Question 25

How do the chondrocytes develop?

Answer 25

Proliferation > Maturation > Growth > Death

Limited supply

Question 26

What is intramembranous ossification?

Answer 26

Direct formation of bones within the mesenchyme by direct osteoblast differentation.

No cartilage template

Examples are flat bones

Question 27

How do bones grow in width?

Answer 27

Osteoblasts on periosteum grow outwards
Osteoclasts on endosteum maintain medullary cavity

Question 28

What is bone modelling?

Answer 28

The bone shape changing in response to the loads imposed on it.

Wolff’s Law - bones adapt based on stress and demands placed on it

Question 29

What is bone re-modelling?

Answer 29

The lifelong cyclical process of bone addition and removal to maintain the structure by repairing microdamage and mineral homeostasis (e.g. exercise).